Memristive memory has the potential for high-density, low-cost storage of data. Some memristive devices, though, are subject to decay or perturbation of state information, which can lead to corruption of data stored in the devices. Other types of memory devices are also known to suffer from decay and perturbation of stored data. For example, binary DRAM uses capacitors that store electric charge representing respective bits and therefore suffers from decay processes (due to charge leakage) that threaten the integrity of stored data. DRAM commonly addresses the problem of charge leakage using refresh cycles to preserve data. Each refresh cycle generally involves reading the stored charge (e.g., the voltage) on a capacitor, deciding whether that charge represents a 0 or 1 bit, then writing the bit value read back to the capacitor. Since the capacitor's charge may have decayed since last being written, the capacitor voltage read is commonly compared to a threshold voltage, and if the voltage read is above the threshold voltage, the capacitor is written to the fully charged state. Otherwise, the refresh operation discharges the capacitor to the fully discharged state.
Use of the same reference symbols in different figures indicates similar or identical items.